Spectrophotometric Determination of Ruthenium with 1-Nitroso-2-Naphthol GWENDOLYN KESSER, R. J. MEYER, and R. P. LARSEN Argonne National laboratory, Chemical Engineering Division,
9700 South Cuss Ave., Argonne, 111.
2-naphthol-3,6-disulfonic acid by Miller, Srivastava, and Good (16). Only a few of these methods (2, 3, 5, 8, 16, 20) would provide the required sensitivity. Because chromogenic reagents which react with ruthenium are, in general, nonspecific, a separation of ruthenium from other sample constituents is required prior to color development if the method is to be applicable to a wide variety of samples. The separation is accomplished either by distillation of ruthenium tetroxide or by extraction of the tetroxide with carbon tetrachloride, and the color development is carried out in an aqueous system. Unfortunately, the formation of the complexes between ruthenium and the chromogenic reagents is quite sloiv in aqueous media a t room temperature, and conditions for obtaining reproducible color development are UEL FOR THE INITIAL core loading of usually quite empirical -Le., heating for the Experimental Breeder Reactora specific time a t a specific temperature I1 (EBR-11) is an alloy of 95% uranium, is required. 2.5oj, molybdenum, 2.0% ruthenium, The separation of the tetroxide by and smaller amounts of zirconium, extraction with carbon tetrachloride appalladium, and rhodium. I n one phase peared attractive t o us because simpler of the processing system being devised equipment is required and the time for EBR-11, molten zinc and zincrequired for the separation is somewhat magnesium alloys are used as solvents less than for a distillation. Especially in the separation of uranium from attractive was the possibility that the ruthenium and other fission products. color development could be performed in I n support of this work, the need arose a nonaqueous system and some of the for a ruthenium analysis sensitive difficulties associated with complex forenough to permit the determination of mation in aqueous systems could thus be 0.005 t o 0.1% ruthenium in zinc and eliminated. zinc-magnesium. Several chromogenic reagents were h wide variety of cahromogenic retested qualitatively for reaction with agents have served as the basis for ruthenium tetroxide in carbon tetraspectrophotometric determinations of chloride; among these were the isomers, ruthenium. Thiourea has been used by I-nitroso-2-naphthol and 2-nitroso-lYaffe and Voigt @ I ) , DeFord (6),and naphthol. The latter has been used by Ayres and Young ( I ) ; thiocyanate by Manning and Menis ( I S ) for determining Forsythe, Magee, and Wilson ( 7 ) , and ruthenium in hydrochloric acid-sulby Belew, Wilson, and Corbin ( 4 ) ; furous acid. KoneEn9 (IO) has predithio-oxamide by -lyres and Young (2); sented the spectra of ruthenium I11 S,.Y' - bis - (3 - dimethylaminopropy1)complexes with both isomers in citric dithio-oxamide by Jacobs and Yoe (9) ; acid solution. Our preliminary tests anthranilic acid by Majunidar and Sen Gupta (12); l-naphthylamine-3,5,'i-tri- showed that ruthenium tetroxide reacts \vith both of these reagents in carbon sulfonic acid by Steele and Yoe (18); tetrachloride and upon subsequent addi2-nitroso-1-naphthol by Manning and tion of a reducing agent, Le., ascorbic Jlenis (13); p-nitrosodimethylaniline by acid, an intense color is produced that Currah, Fischel, McBryde, and Beamish has an absorbance maximum a t approxi(5); 1,4-diphenylthiosemicarbazideby mately 650 mp. Hara and Sandell ( 8 ): 1,lO-phenanThe reaction between ruthenium throline by Banks and O'Laughlin ( 3 ) ; tetroxide, 1-nitroso-2-naphthol, and as4,7 - diphenyl - 1,lO - phenanthroline corbic acid is the basis for the spectroby Vita and Trivisonno (20); l-nitrosoA spectrophotometric method has been devised for the determination of microgram amounts of ruthenium utilizing the reaction between 1 -nitroso-2naphthol and ruthenium tetroxide in Rucarbon tetrachloride solution. thenium is determined b y measurement of the absorbance of its l-nitroso-2naphthol complex a t 645 mp. The molar absorptivity is 18,300. Separation from other sample constituents is accomplished by distilling ruthenium tetroxide and trapping the tetroxide in carbon tetrachloride a t 0" C. The method has been successfully applied to the determination of 0.005 to 0.1 % ruthenium in zinc-magnesium a Iloy s.
F
60440
photometric method presented here. The choice of 1-nitroso-2-naphthol, rather than its isomer, was made on the basis of solubility in CC14, l-nitroso-2naphthol being by far the more soluble of the two. In the initial stages of the work, it appeared that a simple procedure, oxidation of ruthenium to the tetroxide, estraction of the tetroxide with carbon tetrachloride, phase separation, and color development, could be devised. Further investigation proved, however, that quantitative oyidation of ruthenium could not always be achieved a t room temperature. In samples which had contained chloride, the ruthenium was particularly resistant t o osidation, even when oxidation is preceded by prolonged sulfuric acid fuming. To ensure quantitative oxidation of ruthenium, regardless of the species present, a more vigorous oxidation at an elevated temperature was required. Therefore, a distillation was incorporated in the procedure. In the recommended procedure, ruthenium tetroxide is distilled from sodium bismuthate-dilute sulfuric acid (11) and is trapped in carbon tetrachloride at 0" C. -1small fraction of the ruthenium is reduced in the receiver but is easily reoxidized by contacting the carbon tetrachloride with a solution of sodium periodate. Solutions of 1nitroso-2-naphthol and ascorbic acid are added successively to the carbon tetrachloride, and the absorbance of the carbon tetrachloride solution is measured a t 645 mp after overnight color development. EXPERIMENTAL
Reagents. Listed below are the special reagents required. A11 other chemicals used are reagent grade. Sodium sulfate-sulfuric acid solution: 2.031 sodium sulfate-l.OM sulfuric acid. Periodate solution: 5 mg. of sodium periodate per mi. in water. Carbon tetrachloride : Reagent grade carbon tetrachloride was purified by the procedure of Surasiti and Sandell (19)*
1-Kitroso-2-naphthol: Reagent grade 1-nitroso-2-naphthol was purified by the following procedure. Dissolve approximately 10 grams in 500 ml. of carbon tetrachloride. Filter off any VOL. 38, NO. 2, FEBRUARY 1966
0
221
I2 CM
12 CM
I l
-
I P O S I ~ I O NI
Figure 1.
PO5ITION
2
Apparatus for extraction of ruthenium tetroxide
The plane of the capillary is offset from the plane of the flask. The degree of offset Is optional, but should be enough to allow easy monipulation of the standard taper joint
undissolved material. Evaporate to dryness, using an air stream to facilitate evaporation. (Do not heat.) Dissolve in a minimum amount of hot carbon tetrachloride, filter while hot. Recrystallize a t ice-bath temperature. Collect on a sintered glass funnel and air dry. I-Kitroso-2-naphthol solution : 10 mg. of 1-nitroso-2-naphthol per ml. in carbon tetrachloride, made up daily. Any insoluble material is filtered off before making the solution up to volume. Ascorbic acid solution: 1 mg. of ascorbic acid per ml. in absolute methanol, made up daily. Helium gas: grade A, obtained from U. S. Bureau of Mines. Standardization. Solutions of ruthenium(II1 and IV) chloride in 3N HC1 were standardized by carefully evaporating the solutions t o dryness, reducing the ruthenium with hydrogen, and weighing as ruthenium metal. Apparatus. The distillation apparatus is the same as that used by hleyer et al. (16)for the distillation of technetium with the following exceptions: the thermometer well and the heating tape are not necessary; the side arm of the still is wrapped with aluminum foil during the distillation to increase the distillation rate; the standard taper joint between the still and condenser is lubricated with a few drops of 6N HzS04. The design of the extraction apparatus, which also functions as a receiver during the distillation, is shown in Figure 1. Also shown in Figure 1 are the two positions in which the flask is used. With the flask in position 1, solutions are introduced through the capillary by applying a suctjun a t the standard taper joint, Solutions are transferred from the flask by applying air pressure 222
ANALYTICAL CHEMISTRY
a t the standard taper joint. I n position 2, the flask serves as a receiver during distillation. It is kept in this position during the equilibration. A Cary Model 11 Recording Spectrophotometer with matched 2-cm. silica cells was used for all absorbance measurements. However, there is no reason to believe that a less expensive instrument would not be adequate. Cleaning of Glassware. Both the distillation apparatus and the extraction flask are cleaned with hot 5% sodium hypochlorite solution just prior to each use. This treatment is followed by thorough rinsings with distilled (not deionized) water. For a new distillation apparatus, or one that has not been in daily use, more rigorous cleaning is necessary. The apparatus is cleaned by distilling about 5 ml. of concentrated perchloric acid through it. This is followed by thorough rinsings with distilled water. The volumetric flasks are rinsed after each use with methanol (to remove carbon tetrachloride), then with distilled water. They are cleaned with hot sodium hypochlorite, rinsed well with distilled water, and thoroughly air-dried. Soap, detergents or deionized water are never used on any of the glassware. Preparation of Receiver Solution. With the flask in position 1, Figure 1, introduce 15 ml. of carbon tetrachloride through the capillary. (Apply suction briefly before introduction of carbon tetrachloride t o remove any water remaining in the capillary from the cleaning procedure since water interferes in the final step of the color development.) Invert the flask t o position 2, Figure 1. Add 10 ml. of sulfuric acid-sodium sulfate solution and 1 ml. of sodium periodate solution. Equilibrate for about 30 seconds,
avoiding contact of the solution with the capillary. (The addition of periodate and the pre-equilibration should be made just prior to use because periodate is not particularly stable in sulfuric acid.) Procedure. Introduce an aliquot of solution containing 10 to 40 fig. of ruthenium into a 50-ml. beaker. Add 15 ml. of 6N sulfuric acid and evaporate to strong fumes of SO,. Cool, add water, and repeat the fuming to ensure the removal of nitrates and chlorides. (If nitrate is present, a fourfold excess of 12N hydrochloric acid must be added before the solution is heated to prevent ruthenium volatilization.) Transfer the solution with water to the distillation apparatus. If necessary, dilute with water to make the acid concentration 6 N . At this point, prepare the receiver solution as described above. Place the extraction-receiver flask, contained in an ice-bath, in position as a receiver for the distillate. (The tip of the condenser should be as close to the bottom of the flask as conveniently possible to ensure quantitative absorption of the tetroxide.) rldd to the still approximately 1 gram of sodium bismuthate slurried in 6N sulfuric acid. Wrap the side arm of the still with aluminum foil. (This prevents refluxing in the side arm during the distillation.) -4ttach the helium supply and adjust the flow rate to 2 to 3 bubbles per second. Heat the contents of the still with a micro burner and distill about 5 ml. of liquid. Rinse the tip of the still and the condenser with 3 t o 4 ml. of 0.2N sulfuric acid. (The final aqueous volume should not exceed 20 ml.) Pipet 5.00 ml. of 1-nitroso-2-naphthol solution into a 10-ml. beaker and set aside. Stopper the extraction vessel and equilibrate the contents for about 4 minutes. (The equilibration is accomplished with a side-to-side motion such as that of a wrist-action shaker.) While applying a gentle suction, cautiously invert the flask to position l, Figure 1. (Failure to apply suction a t this point allows some of the aqueous phase to enter the capillary.) Discontinue the suction as soon as the aqueous phase is no longer in contact with the capillary. (Prolonged airflow through the system will result in volatilization of ruthenium tetroxide.) Allow the phases to separate completely and immediately introduce the l-nitroso2-naphthol solution through the capillary. (Adequate mixing occurs as the dye is introduced.) Transfer the carbon tetrachloride phase as completely as possible to a dry 25-ml. volumetric flask, being careful not to transfer any of the aqueous phase. Add 1 ml. of ascorbic acid solution, swirling to mix during the addition. Dilute to volume with carbon tetrachloride. Allow the color to develop overnight. Measure the absorbance a t 645 mfi in 2-cm. cells us. a reagent blank. Record the absorbance and calculate the ruthenium concentration from a previously prepared calibration curve.
DISCUSSION AND RESULTS
The fact that ruthenium tetroxide is easily reduced creates handling problems in any procedure in which it is necessary to maintain ruthenium in the octavalent state. At the 200- to 500-pg. level, it is sufficient to employ accepted analytical practices, paying particular attention only to the cleanliness of the glassware (11). At the 10- to 50-pg. level, the cleanliness problem becomes acute, and even traces of reducing impurities can cause significant losses. For this reason, utmost care must be taken to eliminate reducing impurities on glassware, in the sweep gas, and in reagents. Compressed air, a suitable sweep gas for distillations involving 200 pg. or more of ruthenium, cannot be used in the dist,illation of 10 p g . without significant loss by reduction of the tetroxide in the sidearm of the still. The use of extremely pure helium as a sweep gas eliminates this loss. Purity of the reagents which contact ruthenium tetroxide is of particular importance in preventing losses of ruthenium by reduction. The pre-equilibration of the receiver solution with periodate eliminat'es reducing impurities from the aqueous solution, but this short t,reat,nient is not rigorous enough to remove traces of reductants which may be present in the carbon tetrachloride. Impurities in comniercially available carbon tetrachloride, even spectral grade (99 mole yo pure), have in some cases appreciable reduct,ion of ruthenium. (In an extreme case, only 50% of full color was obtained.) The use of the purification procedure of Surasiti and Sandell (19j eliminates this problem. Even though extreme care is taken to exclude reducing impurities from the system, microgram amount,s of ruthenium tetroxide in carbon tetrachloride solution become noticeably less reactive toward l-nit,roso-2-naphthol within five minutes after equilibration with the sodium periodate solution. This behavior, which is apparently caused by a gradual reduction of the tetroxide, is greatly minimized by adding the chromogenic reagent as soon as possible after phase separation. Contact of the tetroxide with ground glass or Teflon promotes the reduction and must be avoided if quantitative recovery is to be achieved. The above observations were influential in the special design of the receiverextraction flask. The use of t'his flask makes it possible to keep t o a minimum the amount of glassware used, to eliminate stopcocks from bhe system, to preequilibrate the carbon tetrachloride with periodate just prior'to use, and to add the chromogenic reagent to the ruthenium tetroxide immediately after the equilibration is completed. Oxidation and Distillation. The strong anionic complexes which ru-
thenium(II1) and (IV) form in acid solutions make analysis of samples from varied sources difficult, if not impossible, unless the analysis is preceded by a vigorous oxidation step, Oxidations performed a t room temperature, prior t o extraction of the tetroxide, were not adequate; neither sodium periodate, argentic oxide, nor ceric sulfate oxidized the ruthenium quantitatively. (Bismuthate was not tested because of the manipulative problems created by solids in the extraction flask.) Only by performing the oxidation to the tetroxide under distillation conditions could quantitative oxidation be ensured. That oxidation a t an elevated temperature is necessary in this procedure is demonstrated by the dada in Table I. The standards which were not oxidized a t 110' C. (and distilled) were fumed with sulfuric acid, transferred directly into the extraction flask, and oxidized FTith periodate. Apparently, even after strong fuming ivith sulturic acid, some of the ruthenium remains complexed and is resistant t o oxidation under the conditions of the extraction. The distillation of ruthenium tetroxide from sodium-bisniuthate (11) has been used routinely in this laboratory for a number of years for larger amounts of ruthenium. I t has the advantages that quantitative distillation is achieved in approximately five minutes and only water is introduced into the receiver with the ruthenium. Ninor modifications of the method for use in this procedure are the result of precautions which must be exercised In handling microgram amounts of ruthenium tetroxide. Carbon tetrachloride alone is not satisfactory as a catch solution because most of the ruthenium is reduced t o the dioxide. The dioxide separates to the interface between the carbon tetrachloride and the water that distills and cannot be quantitatively reoxidized. When both carbon tetrachloride and a solution of periodate are used t o catch the ruthenium, a small fraction of the ruthenium tetroxide is a t times reduced. However, the ruthenium is readily reoxidized t o the tetroxide during the subsequent equilibration. The amount of sodium periodate in the receiver solution was varied from 2 t o 20 mg. with no effect on the final results. The choice of 5 mg. in the procedure was made to ensure an excess of oxidant during both the distillation and the equilibration. Equilibration. Martin (14) has reported a distribution ratio of 58.4 for ruthenium tetroxide between carbon tetrachloride and water. This favorable distribution makes possible an almost quantitative separation of the tetroxide in one extraction. Martin has also reported that the distribution
Table
1. Effect of Distillation Determination of Ruthenium
added, KU rg.
38.5 38.5 38.5 38.5 38.5
38.5
Kot
Distilled distilled
on
found, Ru rg.
38.4 38.1
X
X X
X X X
38.2 32.2 26.1
28.8
is not appreciably affected by the presence of sulfuric acid. Our work has confirmed these data. Belew et aZ. ( 4 ) have reported that a salting agent is necessary t o maintain this distribution when the concentration of ruthenium is less than 2 pg./ml. In their procedure, aluminum nitrate is used. Xartin (14) has demonstrated that sodium sulfate and a number of other salts are equally effective d t i n g agents. Sodium sulfate !vas chosen for this work because of its compatibility rrith the other reagents in the procedure. The equilibration is not an extraction in the strictest sense because the major portion of the ruthenium is already in the carbon tetrachloride a t the end of the distillation. The functions of the equilibration are to provide contact of any reduced ruthenium with the oxidant and to ensure equilibrium distribution of the ruthenium. In addition to periodate, argentic oxide and ceric sulfate were investigated as oxidants. .Irgentic oxide is as effective an oxidant as periodate. However, the 1)resenceof unreacted argentic oxide, ome silver chloride which is apparently formed by reaction of argentic oxide xith carbon tetrachloride, makes the subsequent phase separation difficult. Ceric sulfate is not a satisfactory oxidant; only about 85% of the ruthenium appears in the carbon tetrachloride. Color Development. K h e n 1nitroso-2-naphthol and ascorbic acid are added t o the ruthenium tetroxide simultaneously rather than successively, less than half of the maximum color is produced; when ascorbic acid is added first, no color is produced. The nature of the complex between ruthenium, l-nit~roso-2-naphtho1, and ascorbic acid has not been characterized. Both the purity and the stability of reagent's used in the color development are important factors in obtaining reproducible absorbance measurements. Commercially available l-nitroso-2naphthol must' be purified before use; after purification by the recommended procedure, it is usable for a t least three months. However, solutions of 1nitroso-2-naphthol in carbon tetraVOL. 38, NO. 2, FEBRUARY 1966
* 223
Effect of 1 -Nitro-2-Naphthol on Absorbance Ruthenium taken, 51.2 pg.
Table II.
1-Nitroso2-nap hthol added, mg.
Net absorbance
10 20 40 60
0.675 0.720 0.748 0.748
Table 111. Determination of Ruthenium in Zinc and Magnesium
Magzinc nesium Ruthenium added, added, Added, Found, KO.of mg. mg. pg. av. pg. detns. ’
...
300
...
200 150 150
150 150
33.3 22.2 33.3 16.7
33.9 22.5 33.0 17.0
5 5 5
5
chloride must be made up daily to avoid deterioration of the dye, and any small amounts of insoluble material must be filtered off and discarded. Ascorbic acid is usable as received but the solid is kept refrigerated once the bot’tle is opened. Use of the same ascorbic acid solution over a period of one to two weeks causes a gradual shift of the absorbance peak toward longer wavelengths. The shift is acconipanied by a decrease in niaximum absorbance. Because of the instability of ascorbic acid in methanol the practice of preparing fresh solutions daily was adopted. .A large excess of 1-nitroso-2-naphthol is necessary to obtain maximum absorbance. The effect of l-nitroso-2naphthol concentration on absorbance is shown in Table 11. The amount used in the procedure, 50 mg., was chosen to ensure inasimum color development in the upper range of ruthenium concentration. The effect of ascorbic acid concentration on the color development was investigated, keeping the amount of l-nitroso%naphthol constant a t 50 nig. Varying the amount of ascorbic acid from 0.5 to 5 mg. produced no change in absorbance measurements; however, when the amount of ascorbic acid was increased to 30 mg., a decrease of -5% in absorbance was noted. Because ascorbic acid is added in methanol solution, the effect of methanol was also studied. Varying the amount of methanol from 1 to 5 ml. had no effect on absorbance. Although color development is initially rapid, a period of about 15 hours is required to attain maximum absorbance. Thereafter, the color is stable for several days. For this reason, it is convenient to perform as many determinations as possible on one day and to make absorbance measurements on the following day. 224
0
ANALYTICAL CHEMISTRY
The spectrum of the ruthenium-lnitroso-2-naphthol complex us. a reagent blank is shown in Figure 2. There is no detectable difference in absorbance between a reagent blank and a blank taken through the entire procedure. Measurements made at the absorbance maximum (645 mp) follow Beer’s law in the range 4 to 55 pg. of ruthenium per 25 ml. of carbon tetrachloride. The molar absorptivity is 18,300. The peak in the region of 520 mp does not follow Beer’s law, and the absorbance a t this lvavelength increases slowly but steadily even after the absorbance at 645 mp has become constant. The reason for this behavior is not understood but could conceivably be the result of a l-nitroso2-naphthol-ascorbic acid reaction which is catalyzed by the ruthenium. In the absence of ruthenium, the absorbance a t 520 mp does not change with time. Interferences. Because the distillation of ruthenium tetroxide gives a separation from most other elements, a systematic study of interferences has not been made. Osmium, which would undoubtedly interfere, would be removed as the volatile tetroxide during the sulfuric acid fuming ( 1 7 ) . It is obvious that the presence of any oxidant strong enough to oxidize ruthenium to the tetroxide (e.g., perchloric acid) cannot be tolerated in the sample. Anions such as chloride, bromide, nitrate, and nitrite are removed in the sulfuric acid fuming. It is essential that no aqueous phase be present during the final step of color development. The presence of even a few drops of water in the volumetric flask when the asoorbic acid solution is added causes a precipitate to form, and very little color develops. I n the development and subsequent application of this analysis, it mas noted that particular care had to be taken to avoid the interference of iron introduced into the analysis after the distillation. This iron ivas apparently present in laboratory dust. By using freshly cleaned glassware and working in a particularly clean area, this problem was eliminated. Results. The precision of the method has been tested using standard ruthenium solutions. The relative standard deviation (la) of twenty determinations a t the 30- to 50-pg. level was 1.6% ; the relative standard deviation of seventeen determinations a t the 4- to 25-pg. level was 2.5%. The applicability of the method to the determination of ruthenium in zinc and niagneqium has been demonstrated on both synthetic solutions and actual saniples containing 0.05 to 0.005% ruthenium. The results of analyses of synthetic solutions are given in Table 111. Duplicate metal samples from the EBRI1 processing system were analyzed by performing a single determination on each sample. For 12 sets of duplicate
n7
490
550
750
650
WAVELENGTH, mp
Figure 2. Absorption spectrum of ruthenium- 1 -nitroso-2-naphthol complex 44.9 pg. of ruthenium
samples the relative standard deviation was 1.8y0. This deviation includes any errors involved in sampling and in dissolving the samples. ACKNOWLEDGMENT
The authors thank R. D. Oldham and Carol Kosner for technical assistance in preparing this paper. LITERATURE CITED
(1) Ayres, G. H., Young, F., ANAL. CHEM.22, 1277 (1950). (2) Ibid., p. 1281. (3) Banks, C. ST., O’Laughlin, J. W., Zbid., 29, 1412 (1987). (4) BeIew, W. L., Wilson, G. R., Corbin, L. T., Ibid., 33, 886 (1961). (5) Currah, J. E., Fischd, A., hIcBryde, W. A. E.. Beamish. F. E.. Ibid.. 24. 1980 (1952). (6) DeFord, ’ D. D., Atomic Energy Comm. Rept. NP-1104 (1948). (7) Forsythe, J. H. W., Magee, R. J., Wilson. L., Talanta 3. 324 (1960). (8) Hara; T., Sandell, E. B., Anal. C h m . Acta 23. 65 (1960). (9) Jacobs, W. O.,’ Yoe, J. H., Talanta 2, 270 (1959). (10) KoneEnL, C., Anal. Chim. Acta 29, 423 (1963). (11) Larsen, R. P., Ross, L. E., ANAL. CHEM.31. 176 (1959). (12) Xajumdar, A. K.,‘ Sen Gupta, J. G., Z. Anal. Chem. 178, 401 (1961). (13) Manning, D. L., RIenis, O., ANAL. CHEM.34, 94 (1962). (14) h!artin, F. S.,J. Chem. SOC.1954, p. 2564. (15) Meyer, R. J., Oldham, R. D., Larsen, R. P., ANAL.CHEM.36, 1975 (1964). (16) Miller, D. J., Srivastava, S. C., Good, AI. L., Ibid., 37, 739 (1965). (17) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd Ed p. 700, Interscience, New York, 1959. (18) Steele, E. L., Yoe, J. H., Anal. Chim. Acta 20, 211 (1959). (19) Surasiti, C., Sandell, E. B., Zbid., 22, 261 (1960). (20) Vita, 0. A., Trivisonno, C. F., “Microdetermination of Ruthenium in I
,
c.
Iiranium Compounds,” Goodyear Atomic Corporation, Piketon, Ohio, Atomic Energy Comm. Rept. GATT-1215, Dec. 15 (1964). (21) Yaffe, R. P., Voigt, H. F., J. Am. Chem. SOC.74, 2500 (1952).
RECEIVED for review October 22, 1965. Accepted December 8, 196ij. Work performed under the auspices of the U. S. Atomic Energy Commission under contract Xo. W-31-109-eng-38.
